IRW Posted February 24, 2011 Share Posted February 24, 2011 Hi All, an interesting (seemingly) fact came to my attention today. I always thought the 64 of a Par64 came about due to the lamp being 64/8 of an inch (i.e. 8") in diameter, and the 56 of a Par 56 being 56/8 of an inch in diameter, etc etc. After reading something earlier today, and then roughly calculating it, it would appear that the circumferences of the aforementioned lamps are 64cm and 56cm respectively. I was just wondering how everybody else associates the number with a Parcan? Diameter in inches or circumference in centimeters? Ian Link to comment Share on other sites More sharing options...
Brian Posted February 24, 2011 Share Posted February 24, 2011 ... it would appear that the circumferences of the aforementioned lamps are 64cm and 56cm respectively.Well they would be. It's just one of those odd quirks of maths. Link to comment Share on other sites More sharing options...
adamharman Posted February 24, 2011 Share Posted February 24, 2011 I've only even seen it defined as the diameter in 1/8 of an inch.I think PAR lamps were originally developed for aircraft use in the US so would have been inches rather than cm. Link to comment Share on other sites More sharing options...
karl Posted February 24, 2011 Share Posted February 24, 2011 I've always thought it was eighths of an inch but to be honest, when you think about it, both options seem equally odd. With circles measurements usually refer to the diameter not the circumference. But then why use eighths of an inch rather than simply measure it in inches? Link to comment Share on other sites More sharing options...
adamharman Posted February 24, 2011 Share Posted February 24, 2011 With circles measurements usually refer to the diameter not the circumference. But then why use eighths of an inch rather than simply measure it in inches? maybe just because "38" is quicker than "4 and three quarter inch"? Link to comment Share on other sites More sharing options...
Wol Posted February 24, 2011 Share Posted February 24, 2011 Well they would be. It's just one of those odd quirks of maths. 0.125in * 2.54cm/in * 3.12 = 0.9906cm So yeah, pretty close. I've always treated it as 1/8ths of an inch though. Maybe it's magic ;-) Link to comment Share on other sites More sharing options...
karl Posted February 24, 2011 Share Posted February 24, 2011 With circles measurements usually refer to the diameter not the circumference. But then why use eighths of an inch rather than simply measure it in inches? maybe just because "38" is quicker than "4 and three quarter inch"?True. I was to lazy to work out all the PAR sizes as inches. I just used the three that sprung to mind 64 (8"), 56 (7") and 16 (2"). Link to comment Share on other sites More sharing options...
J Pearce Posted February 25, 2011 Share Posted February 25, 2011 0.125in * 2.54cm/in * 3.12 = 0.9906cm So yeah, pretty close.It's even closer when you actually use pi (3.141). Comes out at 0.997. Link to comment Share on other sites More sharing options...
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